Advances in magnetic resonance imaging (MRI) are driving the development of MRI machines beyond conventional static magnetic field strengths to fields of 4-9 tesla (T). Little is known about the sensory or physiological effects of high strength static magnetic fields on mammals and humans. We have recently discovered that 30 min exposure to a 9.4 T field has behavioral and neural effects in rats. At the behavioral level, magnetic field exposure induced a conditioned taste aversion (CTA) after pairing with the taste of saccharin. CTA has proven to be a sensitive index of visceral perturbation or malaise induced by a treatment; therefore the magnetic field may be experienced by the rat as an aversive stimulus. At the neural level, the same exposure induced specific and significant c-Fos immunoreactivity in brainstem visceral relays (e.g. the nucleus of the solitary tract and parabrachial nucleus) and in vestibular nucluei (e.g., medial vestibular nucleus). Both the behavioral response and the pattern of c-Fos activation are similar to the effects of vestibular disturbances, such as rotation. We hypothesize that the magnetic field activates the rats' vestibular apparatus, causing vertigo; this would b consistent with reports of vertigo and nausea in humans exposed to 4 T fields. These findings suggest that CTA and c-Fos expression can be used in an animal model of the effects of high-strength, static magnetic fields. We propose to determine the sensitivity of rats using the large-bore, high-strength NMR magnets available at the National High Magnetic Field Laboratory. We will make lesions of sensory sites and nerves to determine the pathways for detection of the magnetic field. We will probe the underlying pharmacology with anti-emetics and other drugs that may attenuate the effects of the field. The acute behavioral effects will be measured by observational scoring; aversive or delayed effects will be measured by CTA expression; and the neural response will be quantified by c-Fos expression throughout the brain. These experiments will help predict the effects of future high-strength MRI on humans, and contribute to understanding the neural pathways underlying the effects.